Pretty little murderers
by Crazy.rabbit2
Summary: (AU) Nagisa is the apprentice of the Master Assassain the 'God of death'. Trained to be a killer from a young age, he and his Master take on their most challenging mission yet when they go deep-cover at Kunugigawa academy to find and assassinate a murderer. Will Nagisa be able to hide his blood-lust and be in an ordinary classroom? Will his classmates change his outlook on life?
1. Chapter 1

**Warning! This story contain spoilers for Koro-Sensei's past!**

 **(A/N; Completely random AU were Nagisa is the God of death (IE Koro-Sensei)'s apprentice, and the two of them go to a school as part of a assassination job, where they meet the rest of the cast.**

* * *

The job was simple enough. Sneak in, kill the target and his wife, then slip away into the night.

It was his first time in Japan, but he picked up the language as easily as he always did. It was a pretty low-grade job, killing some unknown politician, but the pay was good and he needed the money, so why not?

Shinobu Koro (which what he was actually called, but was his name according to the forged driving license in his pocket) sat outside his target's house completely hidden in the overgrown bushes.

The house was average size (at least for Japan, compared to the houses in the slums it was a mansion) it was clearly well looked after- The paint looked immaculate without any chips, the car didn't even have a hint of dirt on it, and the flowers all bloomed beautifully. It was a pity this family wasted so much time on making their house look presentable when they'd be dead soon.

" _Nagisa! Why are you always causing trouble for me?_ " A muffled voice female shrieked from somewhere. _Trouble in paradise?_ Koro thought, slightly amused. The next sound left him less amused;  
The harsh sound of a slap then the thud of a small body hitting the ground.

The assassin narrowed his eyes; He was almost entirely desensitized to violence, after all, were he'd grown up a day didn't go by without it. It wasn't uncommon to see children have their legs broken by corrupt police officers, or to be drugged up and used by gangsters.

But that didn't stop Koro from finding child-abuse distasteful.

" _Why can't you do what I say? Why do you have to be so stupid?_ " The shrill voice was fading now, getting harder to hear. Oh well, she'd be dead soon anyway.

It was another hour before Koro made his move- After he'd scanned the area and made a thorough note of the layout and security systems, he went in.

The burglar alarm was simple to dismantle, and the locks were almost too easy to pick. The assassin was in the house within seconds.

The inside was exactly as he imagined; immaculately clean with bland decor. Without making a single sound, the assassin crept through the house, just by listening to the smallest of details, he could tell that the target was in the study and his wife was in their bedroom.

The assassin went into the kitchen, and took one of the families own knives before going upstairs.  
He went for the wife first. She was sat in front of the mirror brushing her dark blue hair. She was a very beautiful woman, but there was something about the look in her eyes that made her seem harsh.

Silently, before she had a chance to even notice him, Koro had entered the room and snuck behind the woman, and slit her throat.  
Her navy blue eyes widened in horror, and her hands grasped at her throat that was now flowing with crimson red blood. She tried to cry for help, but only a gasping, chocking sound came out of her mouth.

"Poor thing." Koro said, his tone convincingly sympathetic (although the look in his pitch black eyes was remorseless). "You don't even realise your about to die until it's too late."

The woman tried to turn to face him, her face was ashen white and her eyes bulging- she was no longer pretty- but instead she slipped backwards of her stool and hit the ground, hardly conscious.

"I bet you can feel the blood pulsing out of you right now.. But pretty soon that pulse is going to feel fainter and fainter." The assassin said, matter-of-factly. Death was a way of life for him, it always had been- the one sure, constant thing you could relay on in life, was death.

 _People die when you kill them._

 _The other person dies so you get to live._

Finally, the woman lay still on top of the carpet soaked with her own blood- _not so immaculate now, is it_ -Koro thought nastily. Then, as he predicted, his target came running into the room, hearing the noise.

"Hiromi?" Mr Shiota called out, as he ran in. "Are you all ri- "

He was cut off as the assassin waiting behind the door sprang at him from behind, forcing the knife into Shiota's hand, then pulling his arm up, causing him to cut his own neck with the knife still soaked with his wife's blood.

Shiota dropped to the floor. Inches from were his wife lay, the knife still held loosely between his fingers. He twitched a few timed before lying still.  
The assassin observed his handiwork- A textbook murder-suicide scene, he thought passively. Just what his client had ordered.  
Koro turned to leave, ready to collect the other half of his pay, when suddenly, he noticed a small blue-haired child standing in the doorway.

"You killed Mummy and Daddy." He said matter of factley

 _Ah_ \- this was where things got complicated.

"You made it look as though Daddy killed Mummy." The kid accused, although there was neither anger nor fear in his voice. For a kid that couldn't be older than six he was remarkably perceptive, and terrifyingly calm. "Are you going to kill me now too?"

"Sorry, kid, can't have any witnesses." Koro told him, the child's eyes widened. The black haired man had never killed a child before.

"Don't!" He said suddenly. "I wont tell. ..So take me with you. And teach me how to be strong like you are."

The assassin cocked his head- What was with children wanting to become his apprentice after they witness him killing their parents? He already had one protege who had come to follow him in the same way.

"Fine- it's Nagisa, right?." Koro finally decided; He liked this kids perceptiveness, his first apprentice was already a big success and plus, he didn't particularly want to murder a child. So this was the logical choice. "But once you're in there's no turning back. Death might be easier."

The assassin held out his hand, and the boy took it.

"What's your name?" Nagisa asked. Koro smiled in that disarmingly dazzling way of his.

"You can call me the God of death."

* * *

9 yrs later.  
"How do you feel about a deep-cover year-long assassination mission?" The God of death asked (although the black haired man's current alias was Cole). Nagisa looked at him with calm blue eyes.

"I think I don't have a choice either way." He said with a slight groan, as he cleaned the blood of his knife in the motel sink. "You've been taking on some weird missions lately, ever since your first apprentice betrayed you and you were almost captured."

"But you'll follow me anyway!" Cole said brightly, but Nagisa didn't miss the way his eyes narrowed slightly at the mention of the betrayal. The God of death still couldn't work out how he had allowed that to happen.

"Unfortunately." The teenager sighed. "So- what are the details?"

"Elite boarding school, string of unfortunate deaths there- The authorities rules them accidents, our client knows better. We're going to find the killers" The master assassin explained.

"We're assassins, not detectives ." Nagisa commented dryly.

"Of course, our client wants us to kill the murderer once we work out who it is. We'll be going in deep-cover" Cole said, smiling. "Besides... It's in Japan."

The blue haired boy perked up at that, looking away from the sink to meet his master's eyes.

"That got your attention." Cole said, triumphantly. "You haven't been to your country or origin for a while, have you? Well.. This'll be your chance to finally attend school there. Who knows? You might even make some friends!"

* * *

 **(A/N: Sorry this is so short, weird and confusing! Please leave reviews to tell me if I should continue or not :p**


	2. Chapter 2

**_(A/N: Sorry if this chapter's a lil boring, it's kind of an establishing chapter. Thank you so much for all the reviews! please keep sending them!_**

* * *

 _"You insolent little brat!" The Orphanage director yelled, kicking the blue haired child in the stomach. "You've only been here a week and you're already causing problems!"_  
 _The boy fell back, hitting the wall and sliding down, he was trembling, a fearful look in his azure eyes._

 _"P-please."_

 _"Heh. Weak little brats like you should just die already. You're going to be in for a world of pain!" The man said, grabbing the whimpering boy by the hair and dragging him over to the other side of the room harshly. The director stopped when he reached a large metal safe that probably cost more than all the beds in the orphanage put together. Swiftly, he typed in a code '4756', and the door swung open. He pulled out an ornate katana that was nestled in with the money in the safe, he unsheathed it, there was a spot of blood on the blade. "Brats are usually a lot less insolent after I carve my initials into their face with this!" The director laughed, he turned to look at the boy's face, expecting that fearful expression he so loved. But instead, the child was smiling, the tears from only seconds earlier disappeared._  
 _The director felt his blood run cold. Bloodlust seemed to radiate off the boy._

 _"W- why're you smiling? Don't you know what's going to happen to you?" The director demanded. The boy's smile just widened, his eyes as deadly as a snakes._  
 _"I'm so glad you opened the safe! My client wanted me to get some documents out of it before I finished the job! I thought you'd be beating me up for much longer." He said, sounding relieved._

 _"F-finish the job!" The Director squawked, his face going puce, before he could say another word, however, the boy in his grip swiped for him._

 _The director didn't feel it at first. Then, his neck started to sting, and he felt something warm gushing out of it. He tried to staunch the bleeding, but it was already too late; He fell back onto the floor with a heavy thud, wheezing out his last breaths. The last thing he saw before he bled out on the dusty orphanage floor was the child's sinister smile, and the bloody razor-blade in between his fingers._

 _"Thanks for helping me make my first solo mission such a big success!"_

* * *

 ** _5 years later_**

* * *

"Your test scores are disappointing, to say the least." The Chairman said to Nagisa, not showing any sign of hesitancy in using sharp words. The condescending smile that he had been wearing since the beginning of the interview remained fixed on his face. "Normally I wouldn't allow a student of your academic level to transfer into my school at all. But giving the rates you're parents are willing to pay, I'll make an exception. But you will, of course, be placed in the E class, with the rest of the lowest scorers in your year."

"Yes sir." Nagisa said, looking down at his feet, feigning embarrassment. Maybe it wasn't entirely feigned; he didn't actually mean to do bad on the entrance exam, he didn't realise how terrible he was at academics since he hadn't been in school properly since he was six. He wasn't like his Master or the first apprentice, who effortlessly learned skills in all subjects without even trying, he realised bitterly.

 _The only thing I'm good at is killing._

 _To hell with Pythagoras theorem, give me a drink to poison._

Infiltrating the school had been simple; Nagisa applied as a student, and the God of Death applied to be a teacher. He got the job easily (something about the recent murders at the school meant he didn't have a lot of competition). His current alias was Shinobu Korro.

 _"I'm re-using the same documents and ID that I used the night I met you!" Korro had said, sounding delighted. Nagisa Oishi (which was his current name, according to his ID) was fairly certain that his Master was just using the alias Korro, because Koro-Sensei was a pun on Koro-Senin (as in un-killable)._

"Classes start tomorrow, you must be present for the assembly, 8:am sharp." Chairman Asano said, his hands behind his back. His suit was immaculately tailored, his office was large and mostly empty asides from education awards that lined the shelves. He gave off a vibe sterile perfection, a man totally devoted to his work. But there were a few details that seemed out of place; The gold leaf shaped-pin on his tie seemed cheap compared to the Chairman's obviously expensive suit. There was a tiny shard of crystal glass on the floor underneath one of the shelves (had one of the awards broke?).

Nagisa noticed all this in an instant. Analysis and observation were his expertise.

"Wait outside my office to be shown to your dormitory." The Chairman said. Nagisa could tell just by looking at the man's mauve eyes that he he his plenty of secrets behind his visage of professionalism.

 _Is he the man who hired us?_

 _Is he the killer?_

The blue haired boy left the room, the ornate wooden doors closing behind him- It felt like a relief to get out of there. Even for an assassin the atmosphere in the office was oppressive.

"So you're new here too?" A petite green-haired girl said, smiling at him. Her hair was pulled up into pigtails, and her hazel eyes were wide and innocent.

"Yeah, but I'm already feeling a little lost." He replied, giving her a shy smile. He was using his usual persona; A little shy, but approachable, weak and kind at the same time so nobody would feel threatened. The type of mild good-hearted person anyone could trust.  
Nagisa had been using personas for so long he wasn't sure he had a personality, just a black void that sucked in life in order to survive.

"I'm already freaking out!" Kayano laughed, "Seriously! Can you believe there were two murders at this place just last semester? If my parents hadn't paid in advance, I wouldn't be going!"

"Yeah," Nagisa agreed. "It's pretty scary, huh?"

The blue haired boy and his Master had already poured over the facts of the murders with excruciating detail; The first Victim was one Kensaku Ono, a homeroom teacher approaching middle age and according to his friends, looking for a girlfriend. He was described in the obituaries as a ' _lovely caring man_ ', but digging a little further revealed he had a reputation as a cruel teacher with a hair-trigger temper. He was murdered in his office March 27th. The assailant was of medium strength (a particularly strong middle-schooler or a average adult male) and had bashed Ono-Sensei's head in brutally with a metal baseball bat. (Shinigami-san had joked rather morbidly that in the pictures, his bashed in skull closely resembled a squashed tomato).

But the most interesting thing about the murder, was what the killer had done after they'd splattered the teacher's brain matter all over the floor; The assailant had gone mad with scissors, leaving cuts all over the victims body, chopping off tufts of hair and carving drawings into the skin with the blade, like a malicious child attacking a barbie doll. The killer had also taken the time to ply out a few of the victims teeth, before apparently getting bored, deciding not to finish the job, leaving the extracted teeth behind, like little bloodied white trophies.

Killing somebody was nothing, Nagisa thought, but it took a special kind of messed up to mutilate the bodies.

Then, like a bad joke, a few weeks later on April 1st, while the school was still reverberating from the shock of the first killing, a second murder occurred; Another teacher, this time a gym one, and ex-military man named AKira Takaoka, unlike Ono-Sensei, this guy was actually well-liked; His gym class students had described him as kind and helpful.

But even he had a sinister side- While he was sweet to his regular classes, there were continuous allegations that he treated the sports teams he managed with harshness bordering on abuse, but no matter what he methods, everyone agreed that he was the reason that the Kunugigawa sports teams did so well.

His body was found in the same condition as Ono-Sensei's, down to the last frightening detail, proving that their was a serial-killer on campus. The only difference was, the time the killer didn't leave the teeth behind.  
The fact the school was still open was a miracle in itself.

"Kayano Kaede and Nagisa Shiota, right? Nice to meet you!" A brown haired boy with golden eyes said, walking over to them, an easy smile on his face. "My name is Yuuma Isogai, I'm the rep for E-class!"  
He seemed almost too perfect, nothing fake about his smile at all. It made the assassin even more suspicious.

"Nice to meet you!" Nagisa and Kayano both chorused with matching smiles.

"Your bags are already in your room, so if you follow me I'll give you a tour of the school- " the brunet said. The school was as grand as Nagisa expected; Big classrooms, state of the art computer rooms, a cafeteria that served only the finest foods. ("But we at E-class get to sort our own food out!" Isogai explained, much to Kayano's disappointment. She was practically drooling over the puddings).

"And this is were the dorms are- " Isogai said, as they reached a staircase. "A-class is that way; They get huge rooms with double beds, and a luxury en-suit bathroom. Their floor has a pretty state-of-the-art game room too." The class rep had a dreamy look in his eyes as he described it. "Just below them in B class, they're pretty much the same, but no games room, then C class, their rooms are smaller still, and D class don't get an en-suit."

"Wait? What about E class?" Kayano cried. Isogai gave an awkward chuckle.

"Well, that's a little off campus- " He started to say, but was interrupted when a tall robust boy with a large nose and mean eyes very purposefully bashed into him, almost knocking the class-rep over.

"Didn't notice you there, Isogai." The guy grunted. His three friends laughed, matching cruel smirks on their faces. "I didn't think there'd be trash lying around in this part of the school. Don't you know you're not suppose to be here?"

"Sorry, Seo-san, I was just showing some new kids around." The brunet said politely. The taller boy scoffed.

"Yeah, I heard about them- You two are so stupid you got moved to E class as soon as you got here, right? That has to be a new record!" Seo said, turning to his three friends; A Lanky boy with half his head shaved, a boy with long black hair, and a plain boy with glasses. "Right, Kyoma, Araki, Ren?"  
The three of them nodded in agreement.

"Yeah, if you scrubs want to stay out of trouble, you better do whatever we say! We're at the top of the A class." Kyoma snickered. He had sallow skin, squinted eyes and long black scraggily hair. He sprayed spit everywhere every time he spoke.

"Okay, they get it." Isogai said, giving Kayano and Nagisa a apologetic look. Kayano looked a mixture of annoyed and nervous, so the assassin faked the same expression. But he'd faced trained killers, war lords and dictators; School bullies didn't phase him.

"But you know, even if they are destined for E class, both these ladies are quite charming in a cute kind of way~" The one with half his head shaved, Ren, said, swanning over to Nagisa and Kayano. "Hey there, if you two are good I might be able to get you in the position of A class' maid."

The assassin felt sick to his stomach, suddenly he wished he was facing trained killers instead.

"No thanks." Kayano said, backing away as Ren tried to caress her face. She looked as creeped out as Nagisa felt, but the A class boy was oblivious.

"What about you?" He asked the blunette.

"I'm a boy!" The assassin cried, indignant (he was in a boy's uniform, it should be obvious!) Ren looked at him, shocked. But before he had a chance to say anything, Isogai lead the two new students away hurriedly, leaving the four A class students glaring at them.

"Sorry about that." Isogai said to them, once they were out of earshot. "I'm sure they don't mean to be so rude."  
Kayano and Nagisa exchanged glances.

"Because that seemed accidental." The green-haired girl said under her breath. Isogai just gave them another one of his dazzling smiles.

* * *

The E-class building was actually separate from the main school; A large run-down wooden shack was the best way to explain it. Nagisa had stayed in worse places, but in the last few years he'd gotten used to relative luxury as their targets got richer and richer.

"I know it doesn't look like much, but it's really quite cosy!" Isogai said, as he lead them through the rickety wooden door. Inside wasn't much better; sparsely decorated, with no air-con, it felt like a sauna even with all the windows thrown open. It was a stark contrast from the luxury of the main school.

So E class really are segregated. Nagisa thought, grimly. This school system is rotten to the core, no wonder people are being murdered.

There were a few other students lining the corridors, most of them looking disinterested and bored, not even looking up as new students passed.

"The girl's room is right over that way, Kayano-san." Isogai said, pointing down the corridor.

"Thanks for the tour, wish me luck!" She said, as she turned and walked away.

"So we share rooms?" Nagisa asked. Great- how was he suppose to go out and investigate when he was sharing with other people? Why had his master thought this mission was a good idea again?  
"Yeah, I think it's nice actually, like a sleepover every night!" The class-rep said. "Plus, it gets kind of cold in the winter since we have no heating, so the more people the better."

"-right." Nagisa said, really not looking forward to this. For one, people his own age tended to annoy him. He'd grown up surrounded by adults, he'd never really been friends with other kids before (Unless you count the first apprentice, but they were more rivals than friends, and the first apprentice was aa few years older than him anyway).

The dorm room was lined with identical wooden bunk-beds that made the place look like an orphanage. Each E-class pupil got a locker to put their stuff in, but it wasn't nearly enough. Clothes and bags were strewn everywhere.

"This the new kid?" A large brute of a boy who towered over the others asked as Nagisa walked in. He was flanked by two cronies; A grinning blonde and a tanned boy with short black dreadlocks. "He don' look like much. What's your name, shrimp?"

"N-Nagisa." The assassin said, pretending to be nervous.

"The name's Terasaka, do what I say if you know what's good for ya." The brute said, before ruffling Nagisa's hair in a way that was probably suppose to be intimidating. "We're already in E class, so there's no point trying to be all goody-two-shoes. So me and my boys know how to have some real fun."

"Right." Nagisa said, giving another one of his shy smiles. He knew Terasaka's type instantly- The classic classroom bully with more brawn than brains who survives by intimidating and picking on the weak. He was like a fish out of water in a fancy academy were the students prize academics over brute strength, Terasaka probably realised that he had less and less power the further away they got from childhood. And judging from the way he smelt, his idea of 'fun' was smoking around the back of the school.

He seemed to have a temper.. _Was he the killer?_ Maybe he lashed out on the teachers because they looked down on his poor grades. It was too early to say.

"Your bed's this way- " Isogai said, pointing to the bed in the corner. He leaned closer to Nagisa, almost whispering in his ear. "And don't let Terasaka and his gang bother you."  
He was so genuinely nice. It was almost confusing.

Being a Saturday, the pupils weren't in lessons. The E-class wasn't welcome in the main building, so those who hadn't snuck of campus just hung around the dorms, half-halfheartedly playing cards. There was a stagnant atmosphere, and everyone seemed lethargic, as if they'd already accepted failure. Everything from the peeling wallpaper to the stains on the ceiling made the place seem dismal.  
It was clear that nobody wanted to be here. Nagisa finished unpacking (mostly just clothes, and a few pieces of special equipment hidden along with it.), and decided to go explore.

He wondered if his Master was at the main building, he had probably landed himself a job teaching a class full of geniuses. There was no point trying to seek him out, however, he'd find Nagisa when the time was right.  
Kunugigawa boarding school had large grounds with a sports stadium, a track field and a swimming pool. The E class was on the edge, however, on the outskirts of the forest.

The assassin wandered towards the thicket of tree's, masking his presence. He didn't even know what he was looking for; Trying to find a murderer would be like looking for a needle in a haystack, and without his Master's direction, he wasn't even sure were to start.

Despite the foliage on the floor, Nagisa walked silently under the canopy of leaves. It was cooler in the shade than in the dorms, at least.  
Suddenly, he felt something prickling on the back of his neck- he was being watched- automatically, he whipped around, and his blue eyes met with mercury.

A red haired boy sat high up on the branches of one of the tree's.

"Do you have psychic powers or something? As soon as I looked at you, you like, sensed it." The boy asked with a grin. Nagisa looked up at him; _damn, he'd acted suspiciously._  
"Just got lucky, I guess." The assassin replied, The red haired boy just jumped down from the tree with almost feline sort of grace, landing squarely next to Nagisa.

"Let me guess; First year student and you're lost." The red head said with a roll of his eyes.

"I'm in my third year!" Nagisa fumed, indignant, feeling himself blush. It may of been his first genuine display of emotion all day. He had always been insecure about his lack of height, even if it did help him lull people into a false sense of safety around him. His master could never understand why he disliked something that helped him kill people.

"Third year?" The taller boy said, raising an eyebrow as if he didn't quite believe. "I don't recognise you. What class are you in?"

"The E-class," Nagisa admitted, shifting from foot to foot. "I just transferred."

"That's brave of you, considering what happened last year. You do know about the murder's, right?" The red head said, mistrust in his voice. There was a flash of excitement in his eyes when he spoke about the murders though, that instantly caught Nagisa's attention.

"Yeah, I know, but my mother wanted me to go to this school no matter what so... " The assassin trailed off and looked away, a sad, forlorn look in his eyes that screamed ' _don't ask me any questions_.' The other boy didn't look entirely convinced, but he let it drop.

"Well, The name's Karma Akabane, I'm in E-class too, but don't expect to see me in lessons or whatever." Karma said, then took a step closer to Nagisa, the assassin took a step away on instinct, backing into a tree. There was something wild under the surface of the red head's eyes.  
"They kicked me into E class for beating the shit out of some asshole, so try not to piss me off, okay." He raised his fist, and when Nagisa flinched away, Karma dropped it with a satisfied smirk, then added. "The last person who pissed me off ended up with his skull smashed in on the floor." Before turning to saunter away.

The assassin maintained his fearful expression until Karma was out of sight, then he allowed himself to smile slightly.  
 _Interesting. He didn't think he'd find a number one suspect in the murder case so quickly._

* * *

 ** _(A/N: SO Nagisa joins the school, and he can already tell there's something wrong with it. I added a flashback of Nagisa's past at the start just so people can see the kind of jobs that he has done. So next chapter, Koro-Sensei will make an appearance and meet his class for the first time!_**

 ** _In other news, I really don't like the name I chose for this fic, so if anyone can think of a better name, please tell me. So far I'm thinking of re-naming it 'The Masquerade'_**


	3. Chapter 3

**Thank you for all the reviews and support, it means a lot! Please continue to review to tell me what you think of the story :D**

* * *

( _Last march)_

Karma sauntered into the office with a look far too relaxed for his current circumstances; He had gotten in trouble for fighting for the twelfth time that year. Well, they called it ' _fighting'_ but despite all his talk his opponent was such a weakling it was more akin to ' _beating up_ '.

"Sup, Sensei." The red head said as he walked in, nodding at his teacher, Mr Kensaku Ono. His devilish grin widened then he nodded at the bandaged older student sat next to him in acknowledgment. "'sup Hakaze."

Hazake glowered at him with a mixture of contempt and fear. His arm was still in a sling after his fight with Karma.

"Akabane, I suggest you adopt an attitude more fitting for the seriousness of this situation." Ono-Sensei growled. He was pissed off, Karma could tell- The guy might even give him a detention.

But Karma wasn't too worried; He liked Ono-Sensei. The guy _got_ him. His parents had been dropping him off at boarding schools since he was eleven. The teachers were always such a pain, trying to force him to follow rule after meaningless rule, then griping when Karma wanted to do his own thing.  
He was labeled as ' _challenging_ ' and treated like a burden by most teachers who saw him as nothing but trouble. But Mr Ono was different; So long as Karma got the grades, the guy let him skip class, and miss homework.

 _"Karma, sure your behaviour is difficult, but you scored 2nd in the whole school, I can't complain."_

He promised to always support the troubled child as long as Karma was in the right.

Karma trusted him. More than any other useless adult, more than any other human, including his parents.

"Okay, so I admit that I might of gone too far, but Hakaze- _Senpai_ was bullying Ritsu- _Senpai_. I think I was right to intervene." The red head said. Ono-Sensei glared at him from over the desk.

"Hazake is the top student in his year! If his injuries effect his test results that could effect my appraisal!" The teacher yelled, slamming his fist into the wooden desk, knocking over a pencil pot. "You think I give a damn if he was picking on some E class nobody like Ritsu Yoshiro!"

Karma stared at his teacher, mercury eyes widened slightly in disbelief. "You said you'd be on my side, sensei- "

"I thought you had potential, Akabane, but you're a good for nothing trouble maker! This incident could effect my pay!" Ono-Sensei yelled, standing up out of his chair. He spat droplets of saliva into the air as he shouted. "Even your good grades can't save you now. I've secured your transfer to E class next year."  
 _E class?! Were all the rejects of the school go?_

 **Grades.**

 **Appraisals.**

 **Pay.**

Karma's expression darkened. He realised he was a fool for thinking this teacher cared about him as a person, that Ono-Sensei ' _got_ ' him. This man only cared about Karma's grades.  
Sensei wouldn't stand by him at all, he'd drop Karma as soon as he became an inconvenience; Just like his parents. Just like all adults.  
Something inside Karma snapped, and a wild rage was unleashed.

"You think I give a _damn,_ you piece of shit!" Karma roared, slamming his fist into the desk so hard the wood splintered all the way through. Ono-Sensei and Hakaze both jumped away.

"You aren't a teacher to me anymore! You're dead to me!"  
He stormed out, not before throwing his chair across the room for good measure. He heard it shatter a window but he didn't give a damn.  
He kicked the door out the way almost hitting it off it's hinges, and shoved his hands in his pockets, not caring that his fist was bleeding.  
"I will fucking burn this school to the ground."

 _A few weeks later, Kensaku Ono was brutally murdered._

* * *

Nagisa was back in the depressing cesspit known as the _'E class lounge'_ , a small room with an assortment of ratty, half broken chairs and one large table covered in various stains.

He was sat playing cards with Isogai, Kayano, and Isogai's blond friend Maehara. He could easily see Kayano's cards, and Maehara's moves were predictable, but still, Nagisa was purposefully loosing (because nobody suspects the weak). He was trying to get as much information out of them as they could, (although Kayano was too new to the school to know much).

"Hmm, so you ran into Karma Akabane?" Maehara said, as he picked up a card. "Everyone says he's scary, but he's alright s'long as you don't piss him off."

"What kind of things piss him off?" Nagisa asked, making himself sound a little nervous. Maehara laughed.

"Don't worry! It's not his style to beat up shrimps like you- no offence." The blonde said, with a slight smile. "He usually goes after bullies, so most of the ' _big five_ ' are terrified of him. He even had serious beef with a teacher once."

Nagisa faked a look of surprise. "A teacher?" He gasped. Meahara dropped his voice.

"Yeah- Ono-Sensei, the guy who died." The blond said in a half-whisper. Isogai gave him a disapproving look. "I know you're not suppose to talk bad about the dead or whatever, but he was a real nasty piece of work. He betrayed Karma and threw him into E class in the first place."  
Nagisa was about to ask more, but suddenly, a hyper-active ball of energy burst into the room.

"Hey there boys and girls!" A voice enthused, everyone looked up to see a black haired man standing in the doorway. "I'm your new teacher, you can call me Koro-Sensei! It's fantastic to meet all of you."

There was a chorus of obligatory ' _nice to meet you'_ s ' and an undercurrent of mutters;

 _'So he's one of those teachers who pretends to care, lets see how long that lasts.'_

 _'Why's he so upbeat- doesn't he know he's been lumped with the worst class'_

 _'What the hell is he wearing?'_

The class' collective self-esteem was so low it was almost tangible, like a big black hole sucking life out of the room. Nagisa looked at his Master curiously- That was a strange persona he had decided on, surely he'd have more time to work on the mission if he was playing the part of 'lazy teacher' instead. He'd also stick out less.

"Okay everyone! I want you all to tell me your names!" Koro-Sensei said with a bright smile "So we can have a proper introduction."

"You know, class doesn't start till Monday, you don't have to be here." A girl with long blonde hair said disdainfully.

"But I really wanted to meet you guys _now_." Koro-Sensei said, a slight whine to his voice. The God of death was wearing black western style teacher's robes and mortar board with a over-sized tie, it made him look strangely out of place in the dank E class setting.  
He had one of those faces that was vaguely good-looking, but still easily forgettable. He could easily use different expressions to become a completely different person.  
Right now with his goofy smile and bright eyes he seemed wild, eccentric and enthusiastic.

"Whatever." The blond haired girl said. "The name's Rio Nakamura. Nice dress by the way."

"These are robes!" Koro-Sensei declared, he pulled out a register from his sleeve. "Okay! Lets see who from class is here! When I call out your name I want you to tell me one thing about you."

 _So my master is going to act as my school teacher; This'll be interesting._ Nagisa thought to himself. Shinigami-san had been a university lecturer before on a mission, but teaching a bunch of rag-tag kids would be very different from that.  
Koro-Sensei read out the register, the kids answered with varying degrees of enthusiasm.

"Hinao Kurahashi- "

" _Here!_ And uh- I like animals!" A girl with short curly hair smiled.

"Ryoma Terasaka."

"Here. And I think this is a stupid idea."

"Nagisa Shiota!"

Black eyes made contact with blue for a fraction of a moment, but neither male made any indication that they knew each other.

" _Here_ \- and I'm new. I hope I get along with everyone." Nagisa said, with a sweet smile. Suddenly, the blond haired girl, Rio Nakamura, grabbed him and pulled him into a hug.

"Aw! You're adorable, of course you'll make friends." She snickered. Nagisa caught Koro-Sensei smirking at him for a fraction of a second over Rio's shoulder.

"Yes! Since your all going to be living and working together over the course of the year, this class will be like family. We'll make sure to support each other ." The teacher said with a dreamy expression in his normally unreadable black eyes.

"Heh- stupid idealist, wait till reality bitch-slaps you in the face." Terasaka grumbled.

"Lets give him a chance." Isogai whispered to him, being his usual nice self. "Anyway, it's almost dinner time- who's on shift to cook today?"

So the E-class had to cook for themselves while the main school got provided for in a fancy cafeteria. Nagisa had to wonder why the Chairman ever thought this school system was a good idea. Maybe he was just a psychopath who wanted to research the effects if inequality?

"Fear not class! I have taken it upon myself to cook dinner for you!" Koro-Sensei declared, that stupid grin on his face. The class looked downright shocked.

"Wow! Really!" Kurahashi said, beaming.

"That bastard better not of messed up our food supplies, if he's burned them imma kill him." Terasaka growled. The teacher paid no heed to the insult, instead he just turned to the class.

"Gather up people from the dorms and follow me!" He said, leading them to the E-class cafeteria (which was just the classroom with the desks and chairs put together). Nagisa had seen his master put on countless personas, but non like this before, his personality just seemed so- .. _Bright._

Once they walked inside, the entire class' face lit up (even Terasaka looked begrudgingly impressed). Nagisa pretended to be surprised also, but of course, by know he knew that anything his master did would be amazing;

A spread of delicious looking food was laid out on the old wooden desks. For a moment, the crispy roast potatoes and aromatic soup almost made the dingy 3-E classroom seem like a fancy restaurant. There was hot-pot, tasty looking fish dishes and more arranged in a buffet.

"Okay class! Dig in!" Koro-Sensei declared. The class practically ran for the food, there was a few _'thank you'_ s' shouted over the crowd. Nagisa followed.

"Wow, Sensei, did you hire people to make this?" Isogai asked, his voice filled with wonder ( _its only food!_ Nagisa thought). The black haired man shook his head.

"No, I made it myself!"

"Whoa! No way!" The class looked impressed. "Are you a chef?"

"No, no, it's just a hobby." Koro-Sensei said, he checked the register. "Let's see- we're still missing Akabane Karma."

At the mention of Karma's name, an uncomfortable, stifling silence filled the class like the teacher had uttered something taboo.

"Don't expect to see him around much, sir." Isogai said, glancing to the side. He looked as if the words left a bitter taste in his mouth. There was another moment of awkward silence. Nagisa caught his master's eye, and the man nodded.

" _Hm_ , We'll see about that." Koro-sensei said quietly, then his smile widened again. "What're you waiting for? Dig in boys and girls!"  
Gradually, the noise level went back up again as people started chatting normally, as if Karma hadn't been mentioned. Nagisa took a plate, and filled it up with food, going to sit with the others as if he was an ordinary student.

* * *

Later that evening, when the other boys were in the dorm room chatting away, (Besides Karma Akabane who was wandering off God knows where.) Nagisa walked through the wooden corridors silently on bare feet, looking through the dirty window at the main building; It looked like a castle from this distance. (Was the killer hiding out there?). It dawned on him how impossible this mission really was. For all he knew, the killer could be in a different country by now.

Suddenly, Nagisa felt a strong arm wrapped around his neck. His instincts kicked in and he automatically went to pull away from his assailant, only to have his wrists grabbed and pulled behind his back also. He could feel his attacker close behind him.  
" _Got you~_." A playful voice whispered into his ear. Nagisa rolled his eyes- He should of known.

"Well done, Master." He said sarcastically, trying in vain to pull his arm free (but the difference in strength was too great). He could feel the black-haired assassin smirking behind him before letting him go.

"You have far too many openings,young Nagisa." The God of death chided. He had changed out of his ridicules teachers robes and was wearing a non-descript dark outfit that blended with the shadows. Nagisa didn't even stumble, instead he just turned around to face his master.

"What about you? You're the one trying to play detective instead of just killing." The blue haired boy said quietly, a skeptical edge to his voice. "And what's with your persona- It'll be more time consuming pretending to be a teacher who cares. It'd be more effective if you were just consistently lazy."

"Short-sighted as ever, Nagisa." Shinigami said, with a shake of his head. "If I want information of these little outcasts, I need to be someone they can trust. Sure, after being let down by adults so often they might be suspicious at first, poor things, but they're so starved for attention and approval, it'll be easy to get them under my thumb."

"How typical of you." Nagisa said- If he wasn't so used to it, Nagisa would find it jarring hearing Koro-Sensei talk about the E class so flippantly after acting so kind to them hours earlier. "But what if the killer isn't in E class."

"I'm certain they are." The God of death said- He was also so damn sure of his own opinion, it was fact to him (to be fair, he'd never been wrong that Nagisa knew of). "But there's one pupil I might have a problem connecting with- That Karma Akabane. I read his file, he doesn't take well to authority."

"That's a pity. He's already my number one suspect." Nagisa said, thinking about their meeting earlier today. The way the red haired boy had looked at him with wild mercury eyes.

"That's why you have to get close to him. Find out the truth so we know if we should kill him!" Koro-Sensei said, then smiled. "It'll be so nice for you to have a friend your own age!"

Something about his tone made Nagisa feel sick. Oh well. He'd just get a confession out of Karma, kill him, then leave this hell hole simple as that. He bowed.

"Yes master." He said solemnly. The black haired man grinned.

"Good, now hurry to bed young Nagisa! I'll be thinking of you sharing a room with a dozen other smelly boys in this shack while I'm sleeping peacefully in my luxury teacher's room in the main building~"  
The blue haired boy frowned and turned to snap at him, but his master had already disappeared into the shadows.

* * *

 **(A/N: So In this story, Koro-Sensei has both his teaching persona, and his ruthless assassin identity, Will he become the mask or stay true to his original motives till the end? Even though he's acting like the Koro-Sensei from the show, there's still a lot of differences; For example, in this story he gave the kids food to win them over (Kind of like Takaoka did) but in the show Koro-Sensei never uses cheap tricks like that and instead lets his actions as a teacher win the kids over.**

 **Nagisa and Karma will soon begin their ill-fated friendship...**

 **So who do people think the killer is so far? leave reviews!**


End file.
